From daa985855dc35dcf78e8f2d86a5f5bcf47ee59c0 Mon Sep 17 00:00:00 2001
From: Alex Crichton <alex@alexcrichton.com>
Date: Mon, 4 May 2026 09:13:48 -0700
Subject: [PATCH] Warn about CLI usage of wasi-common or wasi-threads

This commit adds a warning to the CLI for
https://github.com/bytecodealliance/rfcs/pull/47 being merged to prepare
any would-be users about the upcoming change. This is expected to be
around for 2 versions of Wasmtime, 45.0.0 and 46.0.0, and in 47.0.0 the
warning will become a hard error with the removal of `wasi-common` and
`wasi-threads`.
---
 src/commands/run.rs | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/src/commands/run.rs b/src/commands/run.rs
index 2d69b41d819e..100ab696f01b 100644
--- a/src/commands/run.rs
+++ b/src/commands/run.rs
@@ -1121,6 +1121,18 @@ impl RunCommand {
                         // are enabled, then use the historical preview1
                         // implementation.
                         (Some(false), _) | (None, Some(true)) => {
+                            let flag = if self.run.common.wasi.preview2 == Some(false) {
+                                "-Spreview2=n"
+                            } else {
+                                "-Sthreads"
+                            };
+                            eprintln!(
+                                "\
+WARNING: the `{flag}` flag will be a hard error in Wasmtime 47.0.0 on 2026-07-20. \
+For more information see https://github.com/bytecodealliance/rfcs/pull/47 and \
+please reach out on Zulip with questions.
+                            "
+                            );
                             wasi_common::tokio::add_to_linker(linker, |host| {
                                 host.legacy_p1_ctx.as_mut().unwrap()
                             })?;